The invention which is the subject of this application relates to improvements to the operation of a broadcast data receiver (BDR) and, in particular, to the provision of a video data amplifier and driver circuit therefor.
A BDR is typically one of a large number of the same provided at various locations to receive common data streams broadcast from a remote location by a broadcaster or number of broadcasters. Each BDR typically receives a number of data streams transmitted at different frequencies and to which the BDR selectively tunes in response to user selections, such as to receive a particular television channel. At least one of the data streams includes a video signal carrying video data.
The BDR is typically provided to receive and process video data, audio data and auxiliary data via the data streams. Once received the BDR processes the same so as to allow generation of video, audio and/or auxiliary data such as an Electronic Programme Guide on a display screen and/or speakers as appropriate.
Upon reception the video, audio and auxiliary data, which is typically encoded for the purposes of efficient transmission, is identified, split and processed in accordance with industry standards to allow the decoding and generation therefrom of, for example, the video display to the user.
This invention is primarily directed towards the processing of the video data and, in order to allow the processing of the video data, there is typically provided within the broadcast data receiver amplifiers such as simple discreet amplifiers. However, for the same to be able to receive the video signal, which is typically transmitted and received with a voltage level between the known voltage range of 0 to 1 volt, a DC offset is required to be introduced to the amplifiers to bias the same on the input transistor.
In practise, it is found that the introduction of the DC offset means that any offset voltage is amplified by the gain value of the amplifier and hence appears as an amplified DC offset on the output of the same which is undesirable. Furthermore, the operating temperature of these components can change through time and use and said changes can influence and be influenced by the particular operating environment in which the BDR is located and over which the BDR manufacturer has little or no control other than being able to provide to the user general usage advice and hope that the user adheres to the advice. Thus, in practice any temperature change effects tend to be amplified, and appear as a further DC offset on the output of the amplifier which again is a problem in the operation of the video data amplifier and driver circuit in terms of possible malfunction and incorrect processing of the received video data which in turn can lead to the video display for the user being incorrect.
Conventionally, attempts to solve the problem have foundered in that while a particular circuit or DC supply arrangement may solve a particular problem at particular temperatures of operation of the BDR, if the operating environment conditions change then the conventional solutions do not prove to be a solution in the changed operating environment. In some instances the conventional solutions may exacerbate the problem when the environmental conditions change.
Thus, to date, this type of problem has been regarded as being something which has to be tolerated.
The aim of the present invention is to provide a solution to these problems and furthermore, to provide a solution which is adaptable in that changes in operating conditions of the components can be taken into account.